1. Field of the Invention
The present invention relates to a wireless communication device that performs wireless communications between itself and an object of communication such as non-contact IC card, and carries out various types of data processing.
2. Description of the Related Art
Conventionally, an antenna device having the following structure is known as a wireless communication device. That is, two sets of antenna assembly members each having a plurality of loop antennas placed in the same plane are arranged to face each other while interposing therebetween a passage where communication objects such as wireless tags pass through. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-237720 (Abstract and FIG. 1).) The characteristics of this antenna device are that some of these loop antennas are periodically switched to invert the phases and thus the non-detectible region where a wireless tag is not detected is minimized. It should be noted that the antenna device of this type is utilized as, for example, a gate for preventing shoplifting.
The conventional type of antenna device described above, however, entails the following drawbacks. That is, while an object equipped with a wireless tag passing through between a pair of antenna assembly members, if the wireless tag enters the communication ready area of the antenna device at a relatively low speed, the rise of the voltage generated inside the wireless tag becomes gentle and therefore the power-on-reset function of the wireless tag does not operate properly in some cases. In these case, the communication between the antenna device and the wireless tag is not established, and therefore the reliability of the antenna device is lowered.
Meanwhile, in the case where the phase of particular loop antennas are periodically inverted as in the above-described antenna device, the relay switch and the like need be operated for phase inversion while transmitting carrier waves for communication from the loop antennas. Thus, the switch is operated a number of times while the connection state is on, and therefore the contact point of the switch is caused to labor, thereby shortening the lifetime of the contact point.